textproduct: Albany

WHAT HAS CHANGED

Some adjustments to QPF, aligning closely with latest WPC forecast. This gives amounts as high as 6-8" in isolated portions of the eastern Catskills, and 3-4" across portions of Litchfield County in NW CT.

KEY MESSAGES

1) Multiple rounds of showers/thunderstorms will produce heavy rain this afternoon through Wednesday, especially areas south of I-90 where a Flood Watch is in effect for Flash Flooding for this afternoon through Wednesday afternoon.

2) Despite areas of heavy rainfall, current river forecasts suggest threat for river flooding is low at this time. However, trends will need to be watched, as amounts over 5" would increase the threat, especially across the SE Catskills.

DISCUSSION

KEY MESSAGE 1...

Upper level trough approaches from west today, bringing increasingly upper level diffluent flow and low level convergence which will allow for greater coverage of showers/thunderstorms during this afternoon and evening. Mean cloud layer winds look to be oriented nearly parallel to the low-level jet through 09-12 UTC Wednesday and with freezing heights 12 - 13kft and tall skinny CAPE soundings, efficient warm rain processes capable of producing heavy downpours will be at play. The unidirectional flow also suggests training convection or heavy rain repeatedly impacting a given area, raising concerns for flash flooding. The overall dynamics with this event are quite impressive for July with the NAEFS showing height anomalies 3 to 4 standard deviations below normal as the parent trough closes off into Wednesday with integrated water vapor transport 3-4 standard deviations above normal due to the high V-wind component anomalies and PWATs.

Latest HREFs suggest 3-hour probs for >1" rainfall as high as 70-90% for areas near and west of the Hudson River between 21Z/Tue-00Z/Wed, and 30-70% elsewhere. Similar 3-hour probs for >3" rainfall are 10-30% across the SE Catskills/mid Hudson Valley after 18Z/Tue, and including NW CT after 03Z/Wed, highlighting areas with greatest chances of heaviest rainfall.

It appears that the axis of heaviest rainfall will initially set up for areas near and west of the Hudson River this afternoon/early evening, before shifting east toward the southern Taconics, Berkshires and Litchfield County later this evening through Wednesday morning. This axis of heavy rain with embedded thunderstorms may then lift north into southern VT during Wednesday morning. Additional slow-moving showers/thunderstorms within a developing deformation zone are expected during Wednesday across the region, again producing locally heavy rainfall. Heavy rainfall should finally taper off Wednesday night, however some showers could linger into Thursday and even Friday, especially areas south and east of Albany.

In addition to locally heavy rainfall, will have to watch for isolated stronger thunderstorms this afternoon/early evening, especially across portions of the mid Hudson Valley and NW CT, where 00Z/HRRR suggests MU CAPES potentially reach as high as 1500-2000 J/kg. Can not rule out isolated strong wind gusts from any wet microbursts that occur in these areas.

KEY MESSAGE 2...

Latest HEFS (Ensemble River Forecasts) still suggest only low to very low chances (<10%) of rivers rising above minor flood stage for a few points in the eastern Catskills and southern VT, such as the Williams River at Rockingham and Esopus Creek at Cold Brook. Will have to watch trends with updated NERFC river forecasts today, in case the higher end of QPF (exceeding 5") becomes more likely, which would then increase the potential for at least a few points reaching or exceeding minor flood stage.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

VFR conditions start the TAF period with southerly to southeasterly winds between 3 and 8 knots. Winds increase late this morning into this afternoon ranging between 10 and 15 knots with gusts up to 20 knots at KALB and KPSF. Breezy conditions continue through the end of the TAF period.

Our story shifts from VFR conditions to gradually lowering to MVFR between 14z and 18z due to low cloud ceilings as an approaching weather system arrives. After 18z, MVFR/IFR/LIFR conditions are forecasted to fluctuate for all TAF sites through 29/00z due to gradually lowering cloud ceilings. Visibilities will fluctuate in IFR and LIFR conditions after 29/00z as well due to periods of heavy rainfall/isolated thunderstorms late this afternoon into the overnight hours. Primary concern with thunderstorms this afternoon is lightning, but confidence was too low to include mention of -TSRA in any prevailing line or outside of KPOU, which has been introduced for between 18z and 23z. IFR/LIFR conditions should prevail after 29/06z through the end of the TAF period due to scattered heavy rain showers and low cloud ceilings.

Outlook...

Wednesday Night: High Operational Impact. Definite SHRA...TSRA. Thursday: High Operational Impact. Likely SHRA...TSRA. Thursday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Friday: Moderate Operational Impact. Chance of SHRA...TSRA. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX. Saturday Night: No Operational Impact. NO SIG WX. Sunday: Moderate Operational Impact. Chance of SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...Flood Watch from 2 PM EDT this afternoon through Wednesday evening for CTZ001-013. NY...Flood Watch from 2 PM EDT this afternoon through Wednesday evening for NYZ058>061-063>066. MA...Flood Watch from 2 PM EDT this afternoon through Wednesday evening for MAZ001-025. VT...None.